Composite metal article and method of making same



Oct 1962 D. s. CHISHOLM ETAL 3,056,190

COMPOSITE METAL ARTICLE AND METHOD OF MAKING SAME Filed April 6, 1960 INVENTORS. Doug/cJsSC/m'so/m 00/7 E H0// Patented Oct. 2, 1962 ice 3,056,190 COMPOSITE METAL ARTICLE AND METHOD OF MAKING SAME Douglas S. Chisholm and Don F. Hall, Midland, Mich.,

assignors to The Dow Chemical Company, Midland,

Mich., a corporation of Delaware Filed Apr. 6, 1960, Ser. No. 20,356 5 Claims. (Cl. 29182.5)

This invention relates to a composite article for treating molten iron before it is cast. More particularly the invention relates to a composite article which may be dropped into or otherwise added to molten iron to affect the formation of nodules of free graphite in the so-treated iron. The invention further relates to a method of making said composite article.

Nodular cast iron is well known in the art. Conventionally it is made by adding to cast iron, under the proper conditions, a quantity of a nodulizing agent and inoculating the cast iron. The treatment results in a gray cast iron in which free graphite'appears in compacted or nodular form rather than as flakes. It is also Well known that magnesium is a most eificient nodulizing and deoxidizing agent for molten iron. But its reactivity and low boiling point are such as to render its introduction in the pure or unalloyed state into molten iron a matter of extreme diificulty. Moreover the melting point of the resulting slag is so high as to render its elimination difficult. When an ingot of magnesium is introduced into molten cast iron, the metal vaporizes and produces a large bubble which tends to float rapidly to the surface without reacting with the molten metal. On the other hand, if magnesium is added tomolten cast iron in the form of powder, small bubbles are obtained which do not float out of the iron as'rapi'dly as large bubbles. However, magnesium powder has such great reactivity that it reacts too rapidly with-air at the surface of molten cast iron and hence it is difiicult to use this material for the purpose of introducing magnesium into molten cast 1ron.

To inoculate cast iron, silicon must be present. Further, silicon in combination with magnesium, either as magnesium silicide or magnesium ferrosilicon, attenuates without eliminating, the reactivity of magnesium with oxidizing agents in molten iron. In addition when the silicon is properly proportioned to the magnesium its oxidation product unites with that of magnesium to yield a relatively fusible and hence much more easily eliminated slag.

Magnesium and silicon upon being heated to an elevated temperature combine exothermically to produce a compound Mg Si which may be used alone or alloyed or sintered with additional silicon in the treatment of molten cast iron. Magnesium silicide and its alloys with silicon or ferrosilicon are very brittle and thus are not very practical to handle unprotected in regular foundry operations.

Insofar as We are aware no packaged or encapsulated form of magnesium is commercially available which is generally satisfactory for use in the treatment of molten iron as in effecting nodulization.

It is therefore an object of the invention to provide an article containing magnesium and silicon in improved form for treating molten cast iron in the production of nodular cast iron.

Another object of the invention is to provide a method of making a novel composite article useful in the treatment of molten cast iron in the production of nodular cast iron.

These and other objects and advantages of the present invention will be better understood on becoming familiar with the following description and the appended claims.

The single figure of the appended drawing is an isometric view partly in section of the composite article of the present invention.

In the said drawing it may be seen that the said article consists of a metal core 1 surrounded by a tubular envelope 2 or sheath in the form of a metal pipe.

The objects of the invention are accomplished by reacting, at an elevated temperature, an intimate mixture of magnesium and silicon or magnesium and ferrosilicon within the confines of an elongated envelope of iron or steel, conveniently a conventional iron or steel pipe. The ferrous metal envelope serves both as a reaction vessel and later as a protective cover for the reaction product in the form of a core which is thereby protected from mechanical shock, abrasion and contamination.

In making the article of the invention magnesium and a silicon material selected from the group silicon and ferrosilicon, each in particulated form, preferably passing about a No. 20 sieve (U.S. Sieve Series), are intimately blended and poured into the open end of a conventional iron or steel pipe, such as one about A1 to 1 inch in nominal diameter, but conveniently of about /2 inch diameter, which has been closed at one end as by welding. The powdered mixture is compacted as by tamping and the open end of the pipe is stopped as with a metal plug, or crimped shut. The pipe is then heated in an oven or by means of an acetylene torch to the temperature at which the reaction between magnesium and silicon is initiated. Generally a temperature of 600 C. is sufiicient to initiate the reaction. It is to be preferred that the blended particulated mixture contains from about 0.56 to -1.5 parts by weight of silicon per part of magnesium, although more or less magnesium or silicon may be employed if desired. Compositions containing the larger proportions of silicon tend to sinter at lower temperatures. As pure silicon is relatively expensive it has been found practical and in no way detrimental to use ferrosilicon as the source of silicon in making up the core compositions. The mixtures may contain up to 30 percent by weight of iron as ferrosilicon though at higher iron contents the mixture reacts and sinters less readily.

As an example of the method of making the composite article of the invention, a mixture consisting of 40 percent by weight of atomized magnesium having a particle size passing a No. 20 sieve and 53 percent by weight of silicon powder and 7 percent by weight of powdered iron (to simulate ferrosilicon) each ground to pass a No. sieve, were thoroughly blended together and poured into the open end of a 4 foot length standard steel pipe /2 inch in diameter which had been welded shut at the other end. The blended powder was compacted by tamping and a metal stopper wedged into the open end. The pipe was then heated to a dull red heat or about 600 C. by means of an acetylene torch and then allowed to cool. When the pipe had cooled to room temperature 2.5 inch lengths were cut from the piece and examined. The core was found to be blue-grey in color, porous in appearance, but thoroughly sintered. The core was also securely afiixed to the interior of the pipe as it conformed closely to even slight irregularities in the interior surface of the pipe.

The weight of magnesium per unit length of the article of the invention in unused form may be determined, as described hereinabove, by weighing it and deducting the estimated weight of the pipe, and the weight percent of magnesium in the mixture multiplied by the net weight. Or knowing the analysis of the core material and the weight of core material in a given length of pipe, the weight of magnesium per unit length can be computed.

A typical article of the invention consists of a length of iron pipe, of /2 inch inside diameter, filled with a core material consisting of, in intimate sintered admixture, about 35 percent by weight of magnesium, the balance a ferrosilicon containing 75 percent by weight of silicon. The core material in sintered form has a density of about 2.5 times that of Water. Simple calculations show that the article contains about 0.175 pound of magnesium per linear foot.

The article of the invention is advantageously used t treat a molten ferrous alloy of such composition that if cast after inoculation it would be a gray cast iron. The molten iron is treated in a forehearth or ladle while the melt is at a temperature af about 2600 to 2700 F. Such a melt will ordinarily contain about 1.7 to 5 percent of total carbon, 1 to 5 percent of silicon, 0.02 to 0.2 percent of sulfur, 0.02 to 0.8 percent of manganese and up to 0.15 percent of phosphorus. The melt composition will have been adjusted beforehand, as desired, by well known methods such as flux treatments, or the addition of steel scrap, to bring the composition to the range of 2.5 to 4 percent of carbon and 1.5 to 4.5 percent silicon. A sulfur content above about 0.1 percent may be tolerated in the process, but more magnesium is consumed thereby. More usually the sulfur level is reduced to 0.08 percent or lower by other well known methods before the nodulizing step.

In any event, it is necessary that there be present in the molten ferrous alloy uncombined carbon which can be acted upon by magnesium to form nodular graphite particles within the ferrous metal matrix. The presence of uncombined carbon i assured upon having suitable concentrations of both carbon and silicon in the melt.

To obtain a desirable degree of nodulizing of uncombined carbon it is generally necessary in the case of most ferrous alloys to add suflicient magnesium to leave a residue of 0.003 to 0.05 percent, but more usually 0.0 2 to 0.04 percent by weight of magnesium. Usually a higher residual magnesium content is sought for melts containing higher carbon contents.

Because of the volatility and reactivity of magnesium, the efficiency of addition thereof is relatively low. Generally the added magnesium reacts with the sulfur in the melt to reduce the surfur content to 0.05 to 0.02 percent, or lower. Part of the magnesium also reacts with reducible oxides in the melt. As a rule of thumb it may be expected, in using the article of the invention, that the efficiency of sulfur removal by the magnesium in the article of the invention is about 33 percent based on the theoretical weight relation of magnesium to sulfur in MgS. Further, the retention of magnesium in the melt, over and above desulfurization, may vary from about to percent. The degree of retention must be determined experimentally for a given type alloy and furnace setting.

As an example of the use of the article of the invention a typical 100 pound melt of a ferrous alloy containing 3.2 percent by weight of total carbon, 2.6 percent of silicon, 0.08 percent of manganese, 0.07 percent of phosphorus and 0.08 percent of sulfur is to be treated with the said article to nodularize the graphite and reduce the sulfur content. It is desired to reduce the sulfur content to about 0.02 percent and to obtain a residual magnesium concentration of about 0.04 percent. It is computed that 0.135 pound of magnesium are needed to carry out the desulfurization at an efliciency of 33 percent. Experience with the alloy and furnace setting has shown that the retention of magnesium employed for the additional combined functions of nodulizing the carbon and reducing oxides in the melt is about 10 percent. Thus an additional 0.4 pound of magnesium are required to obtain the desired residual concentration of magnesium.

Nine four-inch lengths of the article of the invention, containing 0.175 pound of magnesium per linear foot, are added to the 100 pound melt while the melt is at a temperature of 2700 F. and supply silicon, to promote graphitization, and the desired amount of magnesium. The sintered Mg-Si-Fe core material reacts quietly with the melt. The melt is stirred and then cast Within 2. to 3 minutes after the nodulizing treatment. If additional time were to elapse before casting of the melt it would be desirable to make a small addition of silicon in amount by weight corresponding to 0.1 to 0.2 percent of the weight of the melt.

The so cast melt is analyzed and examined. The free carbon is found to be in nodular form, rather than in flake form, the sulfur content is found to have been reduced to 0.019 percent and the residual magnesium content of the casting is 0.042 percent.

An advantage of the invention is the simplicity with which the article is prepared, complex manufacturing facilities being unnecessary. As the article is readily prepared with a core of uniform cross section there is the added advantage that semi-skilled workers can be instructed to add given linear lengths of the article rather than given weights to a melt of iron eliminating weighing operations.

What is claimed is:

1. A composite article consisting of a core sheathed by a ferrous metal envelope said core comprising the sintered reaction product of magnesium and a silicon material selected from the group consisting of silicon, ferrosilicon, the proportion of silicon provided by said silicon material ranging from 0.56 to 1.5 parts per part of magnesium in the product and the iron content of the core not exceeding 30 percent by weight.

2. A composite article consisting of a core sheathed by a ferrous metal envelope, the core comprising the sintered reaction product of magnesium and a silicon material selected from the group consisting of silicon and ferrosilicon, the iron content of the core not exceeding 30 percent by weight.

3. A composite article consisting of a core provided with a tubular ferrous metal envelope, said core comprising the sintered reaction product of magnesium and a silicon material selected from the group consisting of silicon, ferrosilicon, the proportion of silicon provided by said silicon material ranging, from 0.56 to 1.5 parts per part of magnesium in the product and the iron content of the core not exceeding 30 percent by weight.

4. The method of making a composite article which comprises heating a closed elongated ferrous metal envelope containing an intimately blended mixture of particulated materials consisting essentially of magnesium and a silicon material selected from the group consisting of silicon and ferrosilicon to at least 600 C. whereby a reaction is initiated between the said magnesium and said silicon material.

5. The method of making a composite article which comprises thoroughly blending a mixture of particulated materials consisting essentially of magnesium and a silicon material selected from the group consisting of silicon and ferrosilicon, the proportion of silicon provided by said silicon material ranging from 0.5 6 to 1.5 parts per part of magnesium in the mixture and the iron content of the mixture not exceeding 30 percent by weight, placing said blended mixture in a tubular ferrous metal envelope closed at one end, closing the open end of said ferrous metal envelope and heating the ferrous metal envelope to about 600 C. whereby a reaction between magnesium and silicon is initiated.

Hardy Aug. 15, 1933 Ammann Apr. 30, 1935 

1. A COMPOSITE ARTICLE CONSISTING OF A CORE SHEATHED BY A FERROUS METAL ENVELOPE SAID CORE COMPRISING THE SINTERED REACTION PRODUCT OF MAGNESIUM AND A SILICON MATERIAL SELECTED FROM THE GROUP CONSISTING OF SILICON, FERROSILICON, THE PROPORTION OF SILICON PROVIDED BY SAID SILICON MATERIAL RANGING FROM 0.56 TO 1.5 PARTS PER PART OF MAGNESIUM IN THE PRODUCT AND THE IRON CONTENT OF THE CORE NOT EXCEEDING 30 PERCENT BY WEIGHT. 